Copper and iron in nutritional immunity

本研究的目的是阐明含铜氧化铁酶（铜蓝蛋白）调控抗细菌感染的营养免疫的机制。为了开发更有效的治疗方法，迫切需要了解营养稳态的机制。营养免疫描述了微生物感染期间改变宿主金属离子稳态的机制。营养免疫的一个重要方面是通过低铁血症（低血浆铁水平）抑制细菌病原体的铁。低铁血症是由肽激素hepcidin调控的，它通过诱导肝细胞、肠细胞和巨噬细胞中铁输出蛋白铁转运蛋白的降解来限制铁向血浆的输出。另一种营养免疫机制涉及高铜血症（高血浆铜水平）。这一过程通过肝脏铜蓝蛋白分泌增加而发生，铜蓝蛋白是一种携带铜的氧化铁酶，在血浆中含有大部分铜。铜被认为有助于通过先天免疫系统的巨噬细胞杀死细菌病原体，然而，铜蓝蛋白在这一过程中的作用尚不清楚。尽管早在60多年前它就被鉴定为急性期蛋白，但在感染期间对铜蓝蛋白的需求仍然未知。作为一种铁氧化酶，铜蓝蛋白通过铁转运蛋白促进铁输出，然而，由于铁转运蛋白降解，在感染期间这种功能是不必要的。因此，铜蓝蛋白在感染期间可能具有其他功能。初步结果表明，铜蓝蛋白敲除小鼠对鼠伤寒沙门菌和金黄色葡萄球菌的全身感染高度敏感。此外，研究发现，铜蓝蛋白敲除小鼠在toll样受体（TLRs）的细菌配体刺激下，血清中促炎细胞因子水平降低，这突出了铜蓝蛋白在TLR信号传导中的可能作用。本研究将采用生物化学和遗传学的方法来了解铜蓝蛋白对营养免疫的作用。AIM1检测铁和铜在铜蓝蛋白缺失小鼠感染超敏反应中的作用。AIM 2旨在了解铜蓝蛋白在巨噬细胞TLR信号传导中的作用。AIM 3研究巨噬细胞或肝细胞表达铜蓝蛋白是否需要宿主免疫。

The objective of this proposal is to elucidate the mechanisms by which the copper­containing ferroxidase, ceruloplasmin, regulates nutritional immunity against bacterial infection. There is an urgent need to understand mechanisms of nutrient homeostasis in order to develop more effective treatments and therapies. Nutritional immunity describes mechanisms that alter host metal ion homeostasis during microbial infection. An important aspect of nutritional immunity is iron withholding from bacterial pathogens via hypoferremia (low plasma iron levels). Hypoferremia is regulated by peptide hormone, hepcidin, which restricts iron export into the plasma by inducing the degradation of the iron exporter, ferroportin in hepatocytes, enterocytes and macrophages. Another mechanism of nutritional immunity involves hypercupremia (high plasma copper levels). This process occurs via increased hepatic secretion of ceruloplasmin, a copper carrying ferroxidase that contains the majority of copper in the plasma. Copper is thought to facilitate killing of bacterial pathogens via macrophages of the innate immune system, however, the role of ceruloplasmin in this process is unknown. Despite its identification as an acute phase protein more than 60 years ago, the requirement for ceruloplasmin during infection remains unknown. As a ferroxidase, ceruloplasmin facilitates iron export via ferroportin, however, this function is unnecessary during infection due to ferroportin degradation. Thus, it is likely that ceruloplasmin has alternative functions during infection. Preliminary results demonstrate that ceruloplasmin knockout mice are highly susceptible to systemic infection by the bacterial pathogens Salmonella typhimurium and Staphylococcus aureus. In addition, ceruloplasmin knockout mice were found to exhibit reduced serum levels of proinflammatory cytokines when challenged with bacterial ligands to Toll­like receptors (TLRs), highlighting a possible role for ceruloplasmin in TLR signaling. In this proposal, biochemical and genetic approaches will be used to understand the contribution of ceruloplasmin to nutritional immunity. AIM1 tests the role of iron and copper on hypersensitivity of ceruloplasmin-­null mice to infection. AIM 2 seeks to understand the role of ceruloplasmin in TLR signaling within macrophages. AIM 3 investigates whether macrophage or hepatocyte expression of ceruloplasmin is required for host immunity.